By way of brief background, cognitive radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently without interfering with licensed users. This alteration of parameters is based on actively monitoring several factors in the external and internal radio environment, such as radio frequency spectrum, user behavior and network state.
In cognitive radio systems, the unlicensed (secondary) users can use the licensed spectrum as long as the licensed (primary) user is absent at some particular time slot and some specific geographic location. However, when the primary user comes back and is present again, the secondary users should vacate the spectrum instantly to avoid interference with the primary user. Hence, continuous spectrum sensing is used to monitor the existence of the primary user. However, sensing performance for a cognitive user is degraded when the channel experiences fading and shadowing.
Accordingly, cooperative spectrum sensing has been proposed to exploit multiuser diversity in sensing process. Conventionally, cooperative sensing is performed in two successive stages: sensing and reporting. In the sensing stage, every cognitive user performs spectrum sensing individually. In the reporting stage, all the local sensing observations are reported to a common receiver and the common receiver makes a final decision on the absence or the presence of the primary user.
Most existing systems focus on the case where observations are reported to the common receiver through perfect channels. However, this is impractical since the channels between the cognitive users and the common receiver are usually subject to fading. As mentioned, prior to accessing the licensed spectrum, cognitive users should detect whether the primary user is present or not. A variety of detection methods have been proposed thus far, but none that are optimal when it is assumed a priori knowledge of the primary user is unavailable.
Accordingly, improved systems and methods are desired for improving sensing performance for cooperative spectrum sensing in the presence of fading and shadowing without assuming a priori knowledge of the primary user. The above-described deficiencies of current designs are merely intended to provide an overview of some of the problems of today's designs, and are not intended to be exhaustive. Other problems with the state of the art of cognitive radio and corresponding benefits of the embodiments described herein may become further apparent upon review of the following description.